A light emitting diode (hereinafter, referred to as an LED) is a semiconductor device that converts current into light. Since a red LED using a GaAsP compound semiconductor was commercialized in 1962, GaP:N-based green LEDs and the like have been used as display light sources of electronic devices including information and communication devices.
Recently, light emitting devices using a nitride-based compound semiconductor have come into the spotlight. One of the reasons is that semiconductor layers emitting green, blue and white light can be fabricated by combining GaN with an element such as In or Al. Such nitride-based light emitting devices are used in various applications such as flat panel displays, traffic lights, indoor lightings, high-resolution output systems and optical communications.
The structure of a commonly used nitride-based light emitting device will be described. As shown in FIG. 1, the nitride-based light emitting device includes an n-electrode 110, a substrate 101, a nitride-based semiconductor layer and a p-electrode 120. The nitride-based semiconductor layer is formed by sequentially laminating an n-type semiconductor layer 102, an active layer 103 and a p-type semiconductor layer 104. The n-electrode 110 and the p-electrode 120 are formed on the n-type and p-type semiconductor layers 102 and 104, respectively.
In the nitride-based light emitting device, when a voltage is applied between the n-electrode 110 and the p-electrode 120, electrons and holes are respectively generated from the n-type and p-type semiconductor layers 102 and 104 and flow into the active layer 103. The electrons and holes are recombined with each other, so that light is emitted from the active layer 103.
To improve light extraction efficiency of the active layer 103, the concentration of electrons generated from the n-type semiconductor layer 102 needs to be similar to that of holes generated from the p-type semiconductor layer 104.
However, in the related art nitride-based light emitting device, the n-type semiconductor layer 102 generally generates electrons having a concentration of 1.0×1019 cm−3, whereas the p-type semiconductor layer 104 generally generates holes having a concentration of 5.0×1017 cm−3 due to a low efficiency of generating holes. Although a larger quantity of p-type impurities may be doped into the p-type semiconductor layer 104, doping efficiency of the p-type impurities may be lowered due to the low efficiency of generating holes as described above.
Accordingly, the resistance of the n-type semiconductor layer 102 is relatively smaller than that of the p-type semiconductor layer 104, and electrons and holes are concentrated in a region of the active layer 103 close to the p-electrode 120. Therefore, when applying current, the current is not uniformly spread into the entire region of the active layer 103, so that electrical characteristics of the nitride-based light emitting device and internal quantum efficiency are deteriorated.
To solve such a problem, in another related art, a transparent electrode 105 is used between the p-electrode 120 and the p-type semiconductor layer 104 by depositing the transparent electrode 105 on the entire surface of the p-type semiconductor layer 104. However, it is difficult to fundamentally solve the problem.